diff --git a/pyproject.toml b/pyproject.toml
index 45b1f34..e932e71 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -53,6 +53,7 @@ select = [
     "RUF100",       # unused noqa (yesqa)
     "UP",           # pyupgrade
 ]
+ignore = ["UP015"]
 
 [tool.zest.releaser]
 create-wheel = true
diff --git a/tzlocal/unix.py b/tzlocal/unix.py
index 4183d4a..117c18d 100644
--- a/tzlocal/unix.py
+++ b/tzlocal/unix.py
@@ -94,7 +94,7 @@ def _get_localzone_name(_root="/"):
     for filename in ("etc/sysconfig/clock", "etc/conf.d/clock"):
         tzpath = os.path.join(_root, filename)
         try:
-            with open(tzpath) as tzfile:
+            with open(tzpath, "rt") as tzfile:
                 data = tzfile.readlines()
                 log.debug(f"{tzpath} found, contents:\n {data}")